Impregnated diamond bit



I Unlted States Patent 1 1 3,537,538

[72] Inventor R0561 E- GQMI'MIX 2,256,092 9/1941 Koebel et a1 175/404XNorth Bay, Ontario, Canada 2,662,738 12/1953 Davis et a1. 175/330 [211App]. No. 826,542 2,833,520 5/1958 Owen 175/379 [22] Filed May 21,19692,996,061 8/1961 Miller 175/330X [45] Patented Nov. 3, 1970 3,127,7154/1964 Christensen... l75/330X 1 Auism Christen-en i m nd rod p y3,127,944 4/1964 Davis 175/3 30x Salt Lake City, Utah Primary Exammer-Dav1d H. Brown Imam. Uuh Attorney Bernard Kriegel [54] NATE) DIAMOND anABSTRACT: A rotary formation drilling core bit, including an r, 3Drawing Figs.

lmpregnated portlon contamlng dlamonds d1spersed 1n a [52] [1.8. CI.175/330, matrix, the inner art of the impregnated portion having a step1 5/379 disposed axially inwardly of the bit face and in which surface-[51 Int. Cl. EZlb 9/36 set diamonds are disposed to create formationcuttings flushed [50] Field of SQII'CII 175/ 329, laterally outwardlyacross the full face of the bit to abrade and 3 125/39 effect itsresharpening by exposing additional diamonds. The rise between the stepand bit face has circumferentially spaced [56] Rehnnm cued ribs forcreating cuttings also flushed across the bit face, the NI D TATE PA E Tflow of flushing liquid being facilitated by the spaces between [75/329the ribs.

122,514 1/1872 Bullock IMPREGNATED DIAMOND BIT The present inventionrelatesto rotary formation drilling bits, and more particularly to bitscontaining diamonds as dominant cutting elements.

Diamond bits of the impregnated type have diamonds dispersed in amatrix. As the bit drills the formation, it is desirable for its matrixto wear away across the entire bit face to expose additional diamondsfor the performance of a cutting action on the formation, until theentire impregnated portion of the bit is consumed, the cutting life ofthe bit then being at an end.

Heretofore, diamond impregnated bits have ceased drilling or cutting theformation despite the fact that a large impregnated portion stillremained. ln core bits, their failure to continue drilling is due to theabsence of continuous self-sharpening of the bit face at the regionadjacent to its inside diameter. The result'is'rapid wear at suchportion of the impregnated bit to the extentthat no diamonds remain atsuch portion for cutting the formation. The entire bit ceases drillingdespite the presence of a large impregnated bit volume ex tendinglaterally outwardly from such worn inner portion to the outside diameterof the bit. Not only does the rapid wear of the inner bit portion causethe entire bit to cease drilling, but the inner ends of the bitwaterways provided in its impregnated portion are covered and closed bythe formation, preventing flushing liquid from passing therethrough tothe exterior of the bit for the purpose of cooling and cleaning the bitand conveying the cuttings from the drilling region upwardly around thebit exterior and toward the top of the hole being drilled.

Thus, prior art diamond impregnated bits have a relatively short, usefullife, requiring replacementalthqltgh the bits still possesses a largediamond impregnated. portion. As noted.

above, bit wear does not occur uniformly across the bit face, butpredominantly at its region adjacent the bit inside diameter.Accordingly, a large portion of the bit is not consumed, but instead iswasted, resulting in large economic loss, which is enhanced by the timerequired to make round trips in a bore hole for the purpose of changingdrill bits;

The dominant wear at the inside diameter region of the bit is due tosuch region not being self-sharpening. The self-sharpening action occursas a result of cuttings formed by the bit acting as an abrasive on thematrix in which the diamonds are embedded, progressively wearing it awayto continuously expose additional diamonds for action upon theformation. Abrasive cuttings have been present at the intermediate andouter portions of the bit face, which are resharpened, but suchresharpened portions are prevented from cutting the formation by theinnermost bit face portion which has been worn to the extent of becomingdevoid of diamonds, and which can do nothing more than slide against theformation without cutting it, much in the nature of an axial thrustbearing.

With the present invention, an impregnated diamond bit is provided whichis'self-shsrpening in its region adjacent to its internal diameter, aswell as at all other regions across the face of the bit. Cuttings areformed in the formation being drilled, which are flushed across theinner portion of the bit face, the abrasive action of the cuttings onthe bit matrix effecting sharpening of such inner portion. The abrasiveformation cuttings are carried across the entire bit face to produce asharpening action across its entire area. Thus, the impregnated portionof the bit wears substantially uniformly across the entire bit face, thebit remaining in a'self-sharpened and useful condition untilsubstantially the entire impregnated mass is consumed. As a result, thebit has a long useful life, being capable of drilling a greater depth ofhole'at a faster rate and in a more economical manner. When theimpregnated bit portion is substantially entirely consumed, itswaterways are shut off or greatly restricted by theformation, advisingthe operator at the top of the bore hole that the bit should be replacedby his noting a considerable rise in pump pressure at the top of thehole.

In general, the present invention includes the provision of a step atthe inside diameter of the impregnated bit portion, in which individualdiamonds are surface-set in spaced relation to one another. Thesediamonds, which are usually larger than thediamondsinthe impregnatedregion of the bit, produce cuttings that are flushed across the insidediameter of the bit face, such cuttings acting as an abrasive upon thematrix and progressivelyexposing the diamonds embedded therein. Thecuttings formed by the surface-set diamonds combine with the cuttingsformed by the exposed diamonds in the face of the impregnated bit to beflushed in greater number across the face of the bit toward the bitoutside diameter, effecting a continuous resharpening of the entire bitface. The impregnated bit portion preferably has ribs projectinglaterally inwardly from the rise of the step, which also producecuttings and form passages therebetween for drilling fluid to carry thecuttings toward the outer bit face, the cuttings and flushing fluidcontinuing to flow laterally outwardly across the entire bit face.

, Waterways are also provided in the bit face from the inside diameterto the outside diameter of the bit, cuttings being flushed through suchwaterways, as well as across the bit face between the waterways. Thesewaterways are substantially as deep as the impregnated portion of thebit. When such portion is virtually all consumed, the formation at theoutside diameter of the bit will shut off flow through the waterways,the sudden increase in fluid pressure signalling the operator that thebit is at the end of its useful life.

This invention possesses many other advantages, and has other purposeswhich may be made more clearly apparent from a considerationof a form inwhich it may be embodied. This form is shown in the drawingsaccompanying and forming part of the present specification. It will nowbe described in detail, for the purposeof illustrating the generalprinciples of the invention; but it is to be understood that suchdetailed description is not to be taken in a limiting sense.

Referring to the drawings:

FIG. 1 is an isometric projection of an impregnated diamond bitembodying the invention, a portion being broken away and disclosing alongitudinal section through part of the bit;

FIG. 2 is an enlarged section taken along the line 2-2 on FIG. 1; and

FIG. 3 is an enlarged section taken along the line 3-3 on FIG. 1.

The specific embodiment of the invention illustrated in the drawings isa core bitfor cutting a core in a bore hole. lt includes a tubularbitshan'k 10 having an upper threaded box 11 for suitable attachment toa core barrel or a tubular drilling string (not shown). The bit shankhas its lower end extending into a backing matrix 12 of annular form andsuitably secured thereto, as by being fused thereto in a furnace at anappropriate temperature. The backing matrix is secured to an annularimpregnated diamond bit portion 13, as by being fused thereto in afurnace at the same time that the steel shank 10 is fused to the backingmatrix 12.

The impregnated portion 13 is of a suitable height or depth, having alower face 14 of any suitable shape, which terminates at the outercylindrical gauge surface 15 of the bit, and also at the innercylindrical gauge surface 16 of the bit. The backing matrix 12 has innerand outer cylindrical gauge surfaces 17, 18 that are the same as theinner and outer gauge surfaces 16, 15, respectively, of the impregnatedbit portion 13.

As noted above, the face 14 of the bit can be made of any suitableshape, depending upon the particular type of formation being drilled. Asspecifically disclosed, it includes a plurality of concentric generallyV-shaped annular ribs 19, the outer rib terminating at the outer gauge15 of the impregnated matrix 13, the inner rib terminating at the rise20 or inner cylindrical wall thatextends upwardly to a step 21 formed inthe impregnated bit portion, this step continuing to the inside diameteror inner gauge 16 of the impregnated bit portion.

The impregnated bit portion 13 consists of a mixture of diamondparticles 22 and a matrix 23, the diamonds being of a suitable mesh andbeing dispersed throughout the entire volume of the matrix.Substantially radial circumferentially spaced waterways 24 extendthrough the diamond impregnated portion from its inner gauge surfaceidto its outer gauge surface 15, the depth of the waterway across theface of the bit being substantially the same as the height of theimpregnated portion, that is, substantially to the backing matrix 12,the inner end of each innerwaterway communicating with a longitudinalwaterway 25 that continues through the backing matrix 12 and being openat its upper end; whereas, the outer end of each waterway 2dcommunicates with a longitudinal or vertical outer waterway 26extendingupwardly through the backing matrix 12 and having an outletopening 27 at its upper end. Thus, a flushing liquid can flow downwardlythrough the steel shank 10, as between it and an inner core barrel (notshown), downwardly through the inner waterways 2S and laterally throughthe waterways 24, and thence through the outer waterways 26, as well asflowing laterally along the inner gauge surfaces 17, i6 and laterallyacross the face M of the bit between the waterways 24. During suchlateral flow across the face 14 of the bit and through the waterways,the flushing fluid carries cuttings therewith, the cuttings also beingflushed from the bit face 14 into the waterways 24 and then upwardlythrough the longitudinal, external waterways 26 to the region above thebacking matrix 12 for continued upward movement around the steel shank land the tubular drilling string (not shown) to the top of the well bore,in a known manner.

As noted above, cuttings have not been available at the face 14 of thebit adjacent its internal diameter for producing an abrasive action onthe matrix 23 at such region, resulting in considerable wear at theinner face portion of the bit, considerably shortening the useful lifeof the bit. In the present case, the step 21 is provided in the bit,diamond cutting elements 30 being set in the face of the step with therequired exposure, these diamonds being circumferentially spaced fromone another. During the drilling action, the impregnated bit portion 13,as well as the surface-set diamonds 30, are producing cuttings, thefluid flowing downwardly along the inside of the shank iu passing alongthe inner gauge l7, id of the bit to carry the cuttings formed by thesurface-set diamonds 3t) longitudinally along the rise 20 and thenlaterally across the face R4 of the bit, the cuttings produced by theimpregnated face also being flushed laterally outwardly across the faceof the bit, all of the cuttings acting as an abrasive against the bitface to gradually wear away the matrix 23 surrounding each diamond 22and exposing the diamonds in the impregnated bit portion for theperformance of the cutting action against the bottom of the bore hole.

Thus, the surface-set diamonds 30 produce cuttings, and such cuttingswill be carried by the flushing liquid laterally outwardly across theinnermost portion or corner 31 of the face 14 of the bit, combining withthe cuttings produced by the face of the bit itself for self-sharpeningaction upon all areas of the bit face, from its inner gauge to its outergauge. The cuttings are also flushed from the face of the bit into thewaterways 24 to reduce the extent of regrinding ofcuttings by the faceof the bit, the cuttings in the waterways being flushed therethrough tothe outer gauge and then upwardly through the longitudinal waterways 26into the annular space between the wall of the bore hole and the steelshank and drilling string thereabove.

To enhance the flow of the circulating fluid toward the drilling face,longitudinal ribs 32 are formed in both the backing matrix 12 and theimpregnated bit portion 13. Additional diamonds 33 or tungsten carbidechips 34, or both, can be embedded in such ribs. Surface-set diamonds 33are preferably contained in each rib 32 substantially to the same extentas the base or bottom 35 of each waterway 2 so that as the step 21 isworn away through loss of diamonds 30 therein, additional diamondcutting elements 33 will be available for insuring the continuousproduction of cuttings at the inner portion of thebit for movementacross the inner corner 31 of the face of the bit, insuring that suchinner corner, and regions adjacent thereto, are reshurpened, as welltill the remainder otthe ltica l4 ofthc bit.

The inwardly projecting longitudinal ribs 32 and the diamonds 33 ortungsten carbide chips 34 set therein produce a core that is slightlyless in diameter than the inside diameter of the inner gauge l6, 17 ofthe impregnated bit portion 33 and of the backing matrix 12. As aresult, space exists between the ribs 32 through which the flushing orcirculating fluid can pass to the step 21, across the step and thenalong the rise 2.0 to the inner edge 31 of the face of the bit, thefluid then flowing laterally outwardly across the bit face to its outergauge surface 15.

To insure the flushing of cuttings across the inner edge 31 of the bitface, so that such inner edge portion will be resharpcncd, together withthe remainder of the bit face, circumferentially spaced longitudinalribs d0 extend laterally inwardly from the rise 20 of the impregnatedportion, these ribs being integral with and formed together with theimpregnated portion 13 and having diamonds embedded in the matrix. Theseribs 40 produce'a diameter of core which is slightly less than thediameter across the rise 20, thus creating waterways or passages throughwhich the cuttings and flushing fluid produced by the surface-setdiamonds 30 can flow across the inner edge 31 and adjacent portions ofthe face 14 of the bit. The ribs 40 also extend longitudinally beyondthe face 14 and then slightly across the face, forming circumferentiallyspaced cutting portions or protuberances 41 that will out against thebottom of the bore hole, these cuttings also being effective forproducing a sharpening action on the inner portion 31 of the face of thebit, and also being flushed with other cuttings across the face of thebit to effect its resharpening.

To insure the cutting of the bore hole to full gauge, I

diamonds 50 or tungsten carbide chips 51, or both, are surface-set inthe outer gauge portionl8 of the backing matrix 12. As disclosed,several rows of diamonds 50 and tungsten carbide chips 51 are embeddedin such gauge portion, the diamonds preferably being in the lowermostrow. if not entirely in such lowermost'row, at least tl crc are somediamonds in such lowermost row, inasmuch as they have a longer cuttinglife than the tungsten carbide chips. Thus, if the outer gauge 15 of theimpregnated portion 13 were to cut a slightly undergauge hole as thedrilling proceeded, the diamonds 50 and tungsten carbide chips 51 in thebacking matrix 12 would ream the hole to its required diameter.

The diamonds 50 and tungsten carbide chips 51 need not necessarily beset in separate planes normal to the bit axis. They can, if desired, beset in helical fashion around the outer gauge portion 18 of the backingmatrix.

As the bit becomes worn during drilling of the bore hole, it is foundthat the lateral outermost part of the impregnated portion 13 wears to agreater extent than the remainder of the drill bit. Although the wearacross the entire face of the bit is found to be substantially uniformfrom its inside diameter M to its outside diameter l5, the outermostregion does, as indicated above, wear to-a greater extent, such thatwhcnthe impregnated portion 13 has been almost entirely consumed, theformation will then extend across the outer ends of the waterways 24 andwill shut off the flow therethrough; that is to say, it will preventcommunication between the radial waterway portions 24 and. thelongitudinal waterways 26 in the outer gauge l5, 18 of the bit. When theflow is shut off, which occurs suddenly, the circulating pressure risessuddenly and will thereby advise the operator that the bit is worn outand requires replacement.

lclairn:

ii. in a rotary drill bit: a body structure having a lower impregnatedportion comprising a mixture of cutting elements and a matrix in whichsaid elements are embedded, said impregnated portion having a drillingface adapted to engage the bottom of the hole in which the bit isoperating anda fluid passage extending longitudinally through said bodystructure and opening into said drilling face, said impregnated portionhaving an inner step adjacent to said fluid passage above said drillingface, and individual cutting elements embedded in said step and adaptedto engage the bottom of the hole.

2. A rotary drill bit as defined in claim 1; said impregnated portionhaving waterways extending from said fluid passage to the periphery ofsaid impregnated portion.

3. A rotary drill bit as defined in claim 1; said cutting elements ofsaid impregnated portion being diamonds.

4. A rotary drill bit as defined in claim 1; said individual cuttingelements being diamonds.

5. A rotary drill bit as defined in claim 1; said cutting elements ofsaid impregnated portion being diamonds; said individual cuttingelements being diamonds.

6. A rotary drill bit as defined in claim 1; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise.

7. A rotary drill bit as defined in claim 1; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise, said ribs havingprotuberances overlapping and integral with that portion of saiddrilling face adjacent to said rise and extending below said drillingface portion.

8. A rotary drill bit as defined in claim 1; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise, said ribs havingprotuberances overlapping and integral with that portion of saiddrilling face adjacent to said rise and extending below said drillingface portion, said cutting elements of said impregnated'portion beingdiamonds, said individual cutting elements being diamonds.

9. A rotary drill bit as defined in claim 1', said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise, said ribs havingprotuberances overlapping and integral with that portion of saiddrilling face adjacent to said rise and extending below said drillingface portion, said cutting ele ments of said impregnated portion beingdiamonds, said individual cutting elements being diamonds, saidimpregnated portion having waterways extending from said fluid passageto the outer periphery of said impregnated portion.

10. in a rotary drill bit: a body structure having a lower annularimpregnated portion. comprising a mixture of cutting elements and amatrix in which said elements are embedded, said impregnated portionhaving an inner gauge surface, an outer gauge surface, and a drillingface adapted to engage the bottom of the hole in which the bit isoperating, said body structure having a fluid passage extending alongsaid inner gauge surface and opening into said drilling face, saidimpregnated portion having a step extending laterally outwardly fromsaid inner gauge surface and disposed above said drilling face, andcircumferentially spaced individual cutting elements embedded in saidstep and adapted to engage the bottom of the hole.

11. A rotary drill bit as defined in claim said impregnated portionincluding circumferentially spaced longitudinal ribs extending laterallyinwardly of said inner gauge surface.

12. A rotary drill bit as defined in claim 10; said impregnated portionincluding circumferentially spaced longitudinal ribs extending laterallyinwardly of said inner gauge surface, said ribs being aligned with andextending upwardly from said individual cutting elements, saidindividual cutting elements extending laterally inwardly of said innergauge surface.

13. A rotary drill bit as defined in claim 10; said impregnated portionincluding circumferentially spaced longitudinal ribs extending laterallyinwardly of said inner gauge surface, said ribs being aligned with andextending upwardly from said individual cutting elements, saidindividual cutting elements extending laterally inwardly of said innergauge surface, and individual cutting elements embedded in said ribs.

14. A rotary drill bit as defined in claim 10; said cutting elements ofsaid impregnated portion being diamonds, said individual cuttingelements being diamonds.

15. A rotary drill bit as defined in claim 10; said cutting elements ofsaid impregnated portion being diamonds, said individual cuttingelements being diamonds. said impregnated portion includingcircumferentially spaced longitudinal ribs extending laterally inwardlyof said inner gauge surface, said ribs being aligned with and extendingupwardly from'said individual cutting elements, said individual cuttingelements extending laterally inwardly of said inner gauge surface.

16. A rotary drill bit as defined in claim 10; said impregnated portionhaving waterways extending from said inner gauge surface to said outergauge surface.

17. A rotary drill bit as defined in claim 10; said impregnated portionhaving waterways extending from said inner gauge surface to said outergauge surface, the bases of said waterways being above said step andlocated substantially at the upper end of said impregnated portion.

18. A rotary drill bit as defined in claim l0; said cutting elements ofsaid impregnated portion being diamonds, said individual cuttingelements being diamonds, said impregnated portion includingcircumferentially spaced longitudinal ribs extending laterally inwardlyof said inner gauge surface, said ribs being aligned with and extendingupwardly from said individual cutting elements, said individual cuttingelements extending laterally inwardly of said inner gauge surface, saidimpregnated portion having waterways extending from said inner gaugesurface to said outer gauge surface, the bases of said waterways beingabove said step and located substantially at the upper end of saidimpregnated portion.

19. A rotary drill bit as defined in claim 10; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally in wardly from said rise.

20. A rotary drill bit as defined in claim 10; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise, said ribs havingprotuberances overlapping and integral with that portion of saiddrilling face adjacent to said rise and extending below said drillingface portion.

21. A rotary drill bit as defined in claim 10; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise, said impregnated portionincluding circumferentially spaced longitudinal ribs extending laterallyinwardly of said inner gauge surface, said longitudinal ribs beingaligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surface.

22. A rotary drill bit as defined in claim 10; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spaced ribsextending laterally inwardly from said rise, said impregnated portionincluding circumferentially spaced longitudinal ribs extending laterallyinwardly of said inner gauge surface, said longitudinal ribs beingaligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surface, said cutting elements of said impregnatedportion being diamonds, said individual cutting cutting elements beingdiamonds.

23. A rotary drill bit as defined in claim 10; said impregnated portionhaving a longitudinal rise extending between said step and drillingface, said impregnated portion including circumferentially spacedribsextending laterally inwardly from said rise, said impregnatedportion including circumferentially spaced longitudinal ribs extendinglaterally inwardly of said inner gauge surface, said longitudinal ribsbeing aligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surface, said cutting elements of said impregnatedportion being diamonds, said individual cutting elements being diamonds,said impregnated portion having waterways extending from said innergauge surface to said outer gauge surface, the bases of said waterwaysbeing above said step and located substantially at the upper end of saidimpregnated portion.

24. A rotary drill bit as defined in claim 10; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces.

25. A rotary drill bit as defined in claim 10; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and'inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidribs being aligned with and extending upwardly from said individualcutting elements, said individual cutting elements extending laterallyinwardly of said inner gauge surfaces.

26. A rotary drill bit as defined in claim it); said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidribs being aligned with and extending upwardly from said individualcutting elements, said individual cutting elements extending laterallyinwardly of said inner gauge surfaces, and individual cutting elementsembedded in said ribs.

27. A rotary drill bit as defined in claim l; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, andindividual cutting elements embedded in in the outer gauge surface ofsaid backing matrix.

28. A rotary drill bit as defined in claim said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidribs being aligned with and extending upwardly from said individualcutting elements, said individual cutting elements extending laterallyinwardly of said inner gauge surfaces, and individual cutting elementsembedded in said ribs, said impregnated portion having waterwaysextending from said inner gauge surface to said outer gauge surface, thebases of said waterways being above said step and located substantiallyat the upper end of said impregnated portion.

29. A rotary drill bit as defined in claim 10; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spaced longitug}dinal ribs extending inwardly of said inner gauge surfaces, saidimpregnated portion having a longitudinal rise extending betwet it saidstep and drilling face, said impregnated portion includingcircumferentialiy spaced ribs extending laterally inwardly from saidrise.

30. A rotary drill bit as defined in claim 10; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidimpregnated portion having a longitudinal rise extending between saidstep and drilling face, said impregnated portion includingcircumferentially spaced ribs extending laterally in wardly from saidrise, said last-mentioned ribs having protuberances overlapping andintegral with that portion of said drilling face adjacent to said riseand extending below said drilling face portion.

31. A rotary drill bit as defined in claim W; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including. circumferentiaily spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidimpregnated portion having a longitudinal rise extending between saidstep and drilling face, said impregnated portion includingcircumferentially spaced ribs extending laterally inwardly from saidrise, said last-mentioned ribs having protuberances overlapping andintegral with that portion of said drilling face adjacent to said riseand extending below said drilling face portion, said longitudinal ribsbeing aligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surfaces.

32. A rotary drill bit as defined in claim ll); said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidimpregnated portion having a longitudinal rise extending between saidstep and drilling face, said impregnated portion includingcircumferentially spaced ribs extending laterally inwardly from saidrise, said last-mentioned ribs having protuberances overlapping andintegral with that portion of said drilling face adjacent to said riseand extending below said drilling face portion, said longitudinal ribsbeing aligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surfaces, said impregnated portion having waterwaysextending from said inner gauge surface to said outer gauge surface ofsaid impregnated portion, the bases of said waterways being above saidstep and located substantially at the upper end of said impregnatedportion.

33. A rotary drill bit as defined in claim iii; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidimpregnated portion having a longitudinal rise extending between saidstep and drilling face, said impregnated portion includingcircumferentially spaced ribs extending laterally inwardly from saidrise, said last-mentioned ribs having protuberances overlapping andintegral with that portion of said drilling face adjacent to said riseand extending below said drilling face portion, said longitudinal ribsbeing aligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surfaces, said cutting elements of said impregnatedportion being diamonds, said individual cutting elements being diamonds.

34. A rotary drill bit as defined in claim 10; said body structurecomprising a shank, and a backing matrix between said shank andimpregnated portion and secured thereto, said backing matrix havingouter and inner gauge surfaces conforming to said outer and inner gaugesurfaces, respectively, of said impregnated portion, said impregnatedportion and backing matrix including circumferentially spacedlongitudinal ribs extending inwardly of said inner gauge surfaces, saidimpregnated portion having a longitudinal rise extending between saidstep and drilling face, said impregnated portion includingcircumferentially spaced ribs extending laterally inwardly from saidrise, said last-mentioned ribs having protuberances overlapping andintegral with that portion of said drilling face adjacent to said riseand extending below said drilling face portion, said longitudinal ribsbeing aligned with and extending upwardly from said individual cuttingelements, said individual cutting elements extending laterally inwardlyof said inner gauge surfaces, said impregnated portion having waterwaysextending from said inner gauge surface to said outer gauge surface ofsaid impregnated portion, the bases of said waterways being above saidstep and located substantially at the l pper end of said impregnatedportion, said cutting elements Jf said impregnated portion beingdiamonds, said individual cutting elements being diamonds.

